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Moriond, La Thuile 18. mar, 201021cmFAST 21cmFAST A Fast, Semi-Numerical Simulation of the High-Redshift 21cm Signal Andrei Mesinger Princeton University.

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Presentation on theme: "Moriond, La Thuile 18. mar, 201021cmFAST 21cmFAST A Fast, Semi-Numerical Simulation of the High-Redshift 21cm Signal Andrei Mesinger Princeton University."— Presentation transcript:

1 Moriond, La Thuile 18. mar, cmFAST 21cmFAST A Fast, Semi-Numerical Simulation of the High-Redshift 21cm Signal Andrei Mesinger Princeton University Mesinger, Furlanetto, & Cen (2010)

2 Moriond, La Thuile 18. mar, cmFAST Motivation We know next to nothing about high-z --> ENORMOUS parameter space to explore Dynamic range required is enormous: single star --> Universe 21cm observations are on LARGE scales Cosmological numerical simulations are computationally expensive and don’t even approach the scales of 21cm observations Most relevant scales are in the linear to quasi-linear regime

3 Moriond, La Thuile 18. mar, cmFAST Philosophy scale Hydrodynamical Numerical Simulations (+RT) Semi-numerical Simulations (independent 3D realizations; FAST!) Analytic Estimates

4 Moriond, La Thuile 18. mar, cmFAST 21cmFAST Portable and FAST! (if it’s in the name, it must be true…) –A realization can be obtained in ~ minutes on a single CPU –Does not require lots of RAM (unlike DexM; Mesinger & Furlanetto 2007 ) Run on arbitrarily large scales Optimized for the 21cm signal Vary many independent free parameters; cover wide swaths of parameter space Calibrated to hydrodynamic cosmological simulations Publically available!

5 Moriond, La Thuile 18. mar, cmFAST 21cmFAST: 3D realizations neutral fraction gas density LOS velocity gradient spin temperature

6 Moriond, La Thuile 18. mar, cmFAST 21cmFAST: 3D realizations neutral fraction gas density LOS velocity gradient spin temperature Compare with hydro sims of Trac & Cen (2007); Trac+ (2008) - coupled hydro, DM, 5 freq. RT, M min ~10 8 M sun, L=143 Mpc

7 Moriond, La Thuile 18. mar, cmFAST Density Fields 1.create linear density and velocity fields (like N- body) 2. perturb linear density field using first-order displacement vectors (Zel’Dovich 1970) 3. recreate evolved velocity field corresponding to the evolved density field OR 1. scale ICs using linear growth factor

8 Moriond, La Thuile 18. mar, cmFAST Density Fields, Pics z= Mpc cells 143 Mpc

9 Moriond, La Thuile 18. mar, cmFAST Density Fields, PDFs

10 Moriond, La Thuile 18. mar, cmFAST Density Field, power spectra -Collapse of gas is delayed with respect to DM -Jeans smoothing, which depends on uncertain ionization + heating history Note scales

11 Moriond, La Thuile 18. mar, cmFAST Ionization Fields Use excursion-set formalism (e.g. Furlanetto et al. 2004), and check if f coll (R filter, x, z) > 1/  starting from some R max --> R cell Use evolved density field to compute f coll Set fractional ionization at last filter step from subgrid sources If desired, include Poisson fluctuations in halo number when computing f coll (look Ma, no halos…) (see Zahn+ 2010)

12 Moriond, La Thuile Pics 18. mar, cmFAST McQuinn+ (2007) Trac & Cen (2007) 21cmFAST see Zahn+ (2010) FFRT-S

13 Moriond, La Thuile Ionization Fields, PDFs 18. mar, cmFAST 0.56 Mpc cells

14 Moriond, La Thuile Ionization Fields, power spectra 18. mar, cmFAST

15 Moriond, La Thuile 18. mar, cmFAST Velocity Gradients, PDFs -nonlinear structure formation creates an asymmetric velocity gradient distribution!

16 Moriond, La Thuile 18. mar, cmFAST How does this impact 21cm power spectra? dimensional ratiodimensionless ratio enhanced power in excess of the geometric (Kaiser) effect (e.g. Barkana & Loeb 2005) Ionized bubbles quickly erase the boosts from velocity gradients on moderate to large scales Mean signal is smaller due to velocity gradients late in reionization: inside-out reionization

17 Moriond, La Thuile 18. mar, cmFAST Full comparison post heating (T s >>T  ) full simDexM (MF07)21cmFAST

18 Moriond, La Thuile 18. mar, cmFAST Full comparison post heating (T s >>T  )

19 Moriond, La Thuile 18. mar, cmFAST Full comparison post heating (T s >>T  )

20 Moriond, La Thuile 18. mar, cmFAST Including X-ray heating and Ly  pumping Numerically integrate outward/back in time, summing the received photons Number density of sources is computed by conditional f coll, again bypassing halo finder

21 Moriond, La Thuile Global evolution 18. mar, cmFAST

22 Moriond, La Thuile Cool Movie 18. mar, cmFAST

23 Moriond, La Thuile 18. mar, cmFAST 21cmFAST; publicly available (Mon): Portable and FAST! (if it’s in the name, it must be true…) –A realization can be obtained in ~ minutes on a single CPU –Does not require lots of RAM (unlike DexM) Run on arbitrarily large scales No need to “run-down” a sim to a particular redshift Optimized for the 21cm signal Vary many independent free parameters; cover wide swaths of parameter space Calibrated to hydrodynamic cosmological simulations download at

24 Moriond, La Thuile 18. mar, cmFAST Deus ex Machina (DexM) Etymology: New Latin Literally: "God from a Machine", translation of Greek theos ek mechanes - a person or thing that appears unexpectedly and provides a contrived solution to an apparently insoluble difficulty (http://www.merriam-webster.com/dictionary/deus%20ex%20machina)http://www.merriam-webster.com/dictionary/deus%20ex%20machina in true marketing fashion, we also offer a “professional” version, with an even more pretentious title: but you will need lots of RAM to take advantage of added benefits, such as…

25 Moriond, La Thuile 18. mar, cmFAST Halo Finder Mesinger & Furlanetto (2007); Mesinger+ (2009, in preparation) z=8.7 N-body halo field from McQuinn et al. (2007)

26 Moriond, La Thuile 18. mar, cmFAST Halo Finder Mesinger & Furlanetto (2007) without adjusting halo locationswith adjusting halo locations

27 Moriond, La Thuile 18. mar, cmFAST Ionizing UV Flux Fields Mesinger & Dijkstra (2008) flux   ∑ L(M halo )/r 2 e -r/ mfp

28 Moriond, La Thuile 18. mar, cmFAST and maybe soon, absorption systems Crociani+ (2009, in preparation) x HI =0.72x HI =0.45x HI =0.18x HI =0 mfp= 10Mpc 20Mpc

29 Moriond, La Thuile 18. mar, cmFAST PR Movie 250 Mpc


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